The present invention relates to an integrally formed parallel four-link mechanism made of a plate-like material, more particularly to a parallel four-link mechanism arranged in such a manner that the mechanical fatigue of hinge sections exposed to stress on their opposed inner surface is decreased.
This type of parallel four-link mechanism, proposed by the same assignee in, for example, Japanese Patent Application SHO No. 63-182063 (corresponding U.S. application: U.S. Ser. No. 375403), has been used in a motion conversion mechanism which employs a piezo electric element.
By referring to FIGS. 1 and 2, an outline of the above motion conversion mechanism will be described hereinafter. The motion conversion mechanism is provided with a base section 3 for supporting one end of a piezo electric element 1 in the compression and expansion directions. A pair of leaf springs 6 and 7 being secured to a main frame 2 extended along the longitudinal direction of the piezo electric element 1 and to a moving member 5 disposed on the other end of the compression and expansion direction of the piezo electric element 1, respectively. An inclining member 8 which links both the leaf springs 6 and 7 is inclined by the deformations of both the leaf springs 6 and 7 according to the expansion and compression of the piezo electric element 1.
In the motion conversion mechanism described above, a parallel four-link mechanism 16 is disposed midway between a sub frame 4 and the moving member 5 which are also placed on the base section 3 of the main frame 2.
The parallel four-link mechanism 16 is elastically deformed according to the expansion and compression of the piezo electric element 1 so as to displace the moving member 5 in parallel with the expansion and compression direction of the piezo electric element 1 and prevent abnormal deformations of the leaf springs 6 and 7 due to the inclination of the moving member 5.
The parallel four-link mechanism 16 is formed with a sheet of leaf spring material elastically deformed by a punching process and a bending process as shown in FIGS. 3 through 5. The parallel four-link mechanism 16 is mainly composed of a pair of link plate sections 17 and a connecting section 26 linked thereto. Each of link plate sections 17 is provided with a first link 18 and a second link 19 which are disposed in parallel to the vertical direction each other, a pair of third link 20 and fourth link 21 which are disposed in parallel to the horizontal direction each other and which are passed between the first link 18 and the second link 19, and hinge sections 22 through 25 which are disposed at connecting sections between the former links 18 and 19 and between the latter links 20 and 21, the width "b2" of hinge sections 22 through 25 is smaller than the width "b1" perpendicular to the lengthwise direction of the links 20 and 21 and the length thereof being "1". In addition, at a lower portion of the first link 18 of the link plate section 17, a connecting plate section 30 is provided. The first link 18 is secured to the sub frame 4. The second link 19 is secured to the moving member 5. The base section of the connecting plate section 30 is secured to the sub frame 4. One end of the connecting plate section 30 is secured to the main frame 2.
Thus, the four hinge sections 22 through 25 on the parallel four-link mechanism 16 in the prior art are formed in the same shape with each other.
When the moving member 5 is deformed according to the expansion of the piezo electric element 1, the hinge section 22 which links the first link 18 and the third link 20 and the hinge section 25 which links the second link 19 and the fourth link 21 are exposed to stress on their opposed inner surfaces. On the other hand, the hinge section 23 which links the second link 19 and the third link 20 and the hinge section 25 which links the first link 18 and the fourth link 21 are exposed to stress on their opposed outer surfaces.
In the parallel link mechanism for the motion conversion mechanism of the prior art described above, when the piezo electric element 1 expands and the moving member 5 is deformed, the amount of stress exposed to each of the hinge sections 22 through 25 become same with each other. However, since the pair of hinge sections 22 and 25 diagonally disposed at round boundaries are exposed to stress on their opposed inner surfaces, the gradation of shape on the outer surfaces of the hinge sections becomes larger than that of the straight sections on the outer surfaces thereof, resulting in a fatigue problem.
As a result of analysis using finite element method, a stress distribution in the conventional parallel four-link mechanism has been obtained as shown in FIG. 6. In the drawing, the stress becomes strong as the numeral increases. The equi-stress curve 5 represents the largest stress and equi-stress curve 4 follows. Thus, it is obvious that a large stress works at the pair of hinge sections 22 and 25 disposed in the diagonal direction and exposed to stress on the opposed inner surfaces.
In addition, since the size of the inner surface of each hinge section is very small, it is difficult to completely remove bur.
Thus, on the opposed inner surfaces of the hinge sections 22 and 25, a crack and thereby a link breakage tends to occur.